Until now, their most bitter enemies have been the odd irksome restaurant critic and cantankerous diner.

But Rick Stein and Jamie Oliver have suddenly found themselves the targets of far more ominous opponents - a self-styled terrorist group.

The little-known Cornwall National Liberation Army has resurfaced for the first time in 20 years to issue a series of murderous threats against the chefs and customers of their restaurants in the county.

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Rick Stein in Padstow, which has been renamed Padstein for the number of properties belonging to the chef

In an email sent to local businesses and newspapers, the CNLA warns of fires and explosions at premises of the "English incomers".

Stein and Oliver have alienated local people, it says, and the chefs' customers will be considered legitimate targets in a campaign to remove the "imperialist English flag of St George" from Cornwall.

Despite the organisation not having the reputation of more fearsome terror groups, police said the threats were being taken "very seriously".

Oxfordshire-born Stein has several successful restaurants in Padstow, while Essex boy Oliver owns the Fifteen Restaurant in Watergate Bay on Cornwall's north coast. The

CNLA, which claims to have "substantial" funding from the U.S., wants Cornwall to be granted independence from the UK based on historic evidence that it is not a county but a separate province.

The group has a history of extremist action, though it has not been heard of on a national level since a series of attacks in the 1980s which included a bomb at a courthouse in St Austell.

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Jamie Oliver in his restaurant

Its email, signed by the "CNLA Directing Council" and sent via an Arabic web-hosting service based in Egypt, says Stein is top of its "operational directives".

"Many local people have approached our activists for assistance against this English incomer," it says.

"His vehicles and those of his clients are bona fide targets for our activists."

The group refers to recent comments by Stein, 60, that locals failed to appreciate the "rosy glow" of publicity he brought to Padstow, which has been nicknamed "Padstein" because of the number of businesses he has there.

The email says: "We feel that the time must now be here for Stein to feel the 'rosy glow' of a real fire and so we declare his businesses, him and his clients and their transport a bone fide target."

Of Oliver, the email states: "We have seen the effects of this arrogant English man in our Country, causing property prices to swell."

Last night, a spokesman for Devon and Cornwall Police said a taskforce had been set up to investigate the threats. He added:

"We take very seriously any threats to commit criminal offences and we will vigorously investigate any pre-meditated or publicised planned criminal activity."

Cornwall County Council leader David Whalley said: "These people are not working in the best interests of the people in Cornwall. This is unacceptable behaviour.

"I understand there may be frustrations about not being able to get affordable housing, but this is not the way to achieve it."

A spokesman for Jamie Oliver's Fifteen restaurant said: "We are very surprised and disappointed by the statement because everything about us is Cornish."